DIGITAL VSB DETECTOR WITH BANDPASS PHASE TRACKER USING RADER FILTERS, AS FOR USE IN AN HDTV RECEIVER

摘要

In a radio receiver for receiving vestigial sideband (VSB) signals including symbol codes descriptive of digital signals, HDTV signals being exemplary of such VSB signals, a tuner provides for selecting one of channels at different locations in a frequency band used for transmitting such VSB signals. The tuner also includes mixers for performing plural conversion of the selected channel to a final intermediate-frequency signal, which is digitized by an analog-to-digital converter. A phase tracker, operative on narrow-bandpass filtered portions of the digitized final intermediate-frequency signal centering on its carrier frequency, suppresses an imaginary portion of the final intermediate-frequency signal, arising from multipath distortion or from phase incoherency in local oscillations used during frequency conversion. A digital controlled oscillator in the phase tracker supplies digital descriptions of the carrier wave for the final intermediate-frequency signal to a synchronous detector, which synchronous detector detects the real portion of the digitized final intermediate-frequency signal in accordance with those digital descriptions of the carrier wave. A pair of all-pass digital filters, which exhibit a constant .pi./2 difference in phase response for the digitized bandpass signals and are designed based on Jacobian elliptic functions as described by C. M. Rader, are used in the phase tracker for generating the real and imaginary portions of the digitized final intermediate-frequency signal.